Various types of equipment, instruments, etc., used in hospitals, laboratories, and the like are sterilized for disinfection and killing bacteria and fungi. Plasma treatment is known as a sterilization treatment (see, for example, “3.3.1 Sterilization Experiment Using Low-pressure Discharge Plasma” in Non-patent Literature 1).
Plasma treatment is used not only for sterilization treatment but also for plasma dry-etching and plasma cleaning of the surface of articles to be treated, such as electronic parts, in the production of semiconductor devices.
Plasma dry-etching generally comprises applying high-frequency power to electrodes placed in a reaction chamber that is a vacuum vessel, plasmarizing a gas for generating plasma introduced in the reaction chamber, and etching a semiconductor wafer with high precision. Plasma cleaning removes metal oxides, organic substances, burrs, etc., deposited on or adhering to the surface of articles to be treated, such as electronic parts, to improve bonding or wettability of solder, thus enhancing bonding strength and improving adhesion to a sealing resin and wettability.
A method using a plasma treatment detection indicator comprising a color-changing layer that changes color in a plasma treatment atmosphere is known as a method for detecting the completion of these plasma treatments.
For example, Patent Literature 1 discloses an ink composition for detecting plasma treatment, the composition comprising 1) at least one of anthraquinone colorants, azo colorants, and phthalocyanine colorants, and 2) at least one of binder resins, cationic surfactants, and extenders, wherein a gas for generating plasma used in the plasma treatment contains at least one of oxygen and nitrogen; Patent Literature 1 also discloses a plasma treatment detection indicator comprising a color-changing layer formed from the ink composition formed on a base material.
Patent Literature 2 discloses an ink composition for detecting inert gas plasma treatment, the composition comprising 1) at least one of anthraquinone colorants, azo colorants, and methine colorants, and 2) at least one of binder resins, cationic surfactants, and extenders, the inert gas containing at least one selected from the group consisting of helium, neon, argon, krypton, and xenon; Patent Literature 2 also discloses a plasma treatment detection indicator comprising a color-changing layer formed from the ink composition formed on a base material.
These plasma treatment detection indicators are useful indicators that allow the completion of plasma treatment to be determined from the color change of the color-changing layer.
However, there are indications that with these plasma treatment detection indicators, the color change of the color-changing layer may be slow and the completion of plasma treatment may not be determined accurately, especially when the plasma intensity is set to be low in reduced-pressure plasma or when atmospheric-pressure plasma, which generally has plasma intensity lower than that of reduced-pressure plasma, is used. Accordingly, there is room for improvement in color change properties.
Thus, in view of the problems described above, there is demand for the development of a plasma treatment detection indicator that enables the completion of plasma treatment to be confirmed from the color change of a color-changing layer by controlling the color change rate, regardless of whether the type of plasma is reduced-pressure plasma or atmospheric-pressure plasma, and regardless of the degree of plasma intensity; also demanded is an ink composition for detecting plasma treatment for forming the color-changing layer.